Drive systems for motor vehicles are continuously monitored for malfunctions. Thus, for example, monitoring of the motor vehicle with regard to an unintended acceleration is generally carried out by continuous torque monitoring by the control unit, or by acceleration monitoring based on a vehicle acceleration ascertained from the wheel speeds. One alternative is acceleration monitoring based on a measurement of a longitudinal acceleration of the motor vehicle with the aid of an acceleration sensor.
When an inertial sensor, for example, is used as the acceleration sensor, accelerations which are exerted by external forces may be measured. Naturally, however, accelerations which are caused by gravitational force cannot be measured using this measurement principle. In other words, there is a difference between monitoring of the vehicle acceleration with the aid of an acceleration sensor and mere evaluation of wheel speeds, in that the measurement of the acceleration with the aid of the acceleration sensor does not include the gravitational influence during uphill or downhill travel. In particular, when an acceleration sensor is used, a continuous speed of the vehicle during uphill or downhill travel also results in an acceleration value that is necessary to counteract the gravitational influence. This sensor behavior is advantageous for vehicle monitoring, since the driver takes a possible acceleration or deceleration due to gravitation into account in his/her driving input, and the engine control system thus also appropriately adapts the driver input torque.
In addition, an acceleration sensor that is used for monitoring a vehicle acceleration must be calibrated, adjusted, or adapted in order to reduce its tolerances. If the calibration is carried out, for example, with the aid of a vehicle speed which is measured via the wheels, calibration errors may result, since the speed signal of the wheels includes the gravitational influence, but the sensor does not.
In order to reduce the gravitational influence during a calibration during uphill or downhill travel, such an adaptation of the acceleration sensor must be carried out over a fairly long period of time. However, any height difference between the initial point and end point of the calibration measurement results in a residual error which adversely affects the sensor calibration.
German Published Patent Application No. 19 812 426 relates to a method for calibrating an onboard autonomous acceleration sensor based on an integrated course angle which is ascertained with the aid of a navigation system.
German Published Patent Application No. 10 2004 003877 provides a vehicle response detector which includes an autonomous acceleration sensor and a radio navigation position finding unit. With the aid of a calibration unit, detection information may be calibrated by the autonomous acceleration sensor by utilizing position information from the radio navigation position finding unit.
European Patent No. EP 1 315 945 relates to a vehicle navigation system in which orientations of axes of acceleration sensors are corrected with respect to axes of a frame of a vehicle.